Electrically conducting polymer and production method and use thereof

ABSTRACT

The invention provides a production method of a conductive polymer, comprising a step of blending a polymer in a state of a melt viscosity of 600 Pa·s or less at a shear rate of 100 s −1  with a vapor grown carbon fiber in 1 to 15 mass at a mixing energy of 1,000 mJ/m 3  or less, and a conductive polymer obtained thereby. Preferably, a vapor grown carbon fiber used has an outer fiber diameter of 80 to 500 nm, an aspect ratio of 40 to 1,000, a BET specific surface area of 4: to 30 m 2 /g, a do02 of 0.345 nm or less according to an X-ray diffraction method, and a ratio (Id/Ig) of 0.1 to 2 wherein Id and Ig each represent peak heights of a band ranging from 1,341 to 1,349 cm −1  and a band ranging from 1,570 to 1,578 cm −1  respectively, according to a Raman scattering spectrum. According to the invention, an excellent conductivity can be attained by compounding vapor grown carbon fiber in a smaller amount than in a conventional method.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is an application filed pursuant to 35 U.S.C. Section 111(a) withclaiming the benefit of U.S. provisional application Ser. No. 60/500,237filed Sep. 5, 2003 and U.S. provisional application Ser. No. 60/546,973filed Feb. 24, 2004 under the provision of 35 U.S.C. 111(b), pursuant to35 U.S.C. Section 119(e)(1).

TECHNICAL FIELD

The present invention relates to a production method of an electricallyconductive polymer using vapor grown carbon fiber as a conductivefiller, more specifically to a production method of an electricallyconductive polymer having vapor grown carbon fiber compounded therein ina smaller amount but exhibiting an electric conductivity which is ashigh as or higher than conventional electrically conductive polymers.Also, the present invention relates to an electrically conductivepolymer produced by the method excellent in mechanical strength andconductivity, and to use of the polymer.

BACKGROUND ART

Conventionally, blending a thermoplastic resin, which per se iselectrically insulative, with a conductive filler is a long-knowntechnique for imparting characteristics such as conductivity andantistatic property to the resin, and therefore, a variety of conductivefillers are employed for this purpose.

When a conductive substance is incorporated into resin or rubber whichis generally an insulator, for the purpose of imparting conductivity, aphenomenon is observed that the conductivity, which only graduallyincreases as the filling amount of the conductive substance increases,drastically increases at the point when the filling amount reaches acritical amount and then again gradually increases, so-called“percolation”, a characteristic transition from an insulator to aconductor. It is explained that a three-dimensional network formed inthe insulator matrix by an electric conductor causes the phenomenon. Thecritical amount is called “percolation threshold value” (hereinafterreferred to simply as “threshold value”). The threshold value is knownto virtually depend on the type of the resin serving as a matrix and thetype of the conductor.

Examples of generally employed conductive fillers include carbonaceousmaterials having graphite structure such as carbon black, graphite,vapor grown carbon fiber (hereinafter abbreviated as “CF”), and carbonfiber; metallic materials such as metallic fiber, metallic powder, andmetal foil; metal oxides; and metal-coated inorganic fillers. Amongthem, in order to attain high conductivity through incorporation of asmall amount of conductive filler, use of carbon black or hollow carbonfibrils has been encouraged.

However, when the amount of conductive filler is increased so as toattain high conductivity, melt fluidity of the aforementioned resincomposition decreases, leading to difficulty in molding and readilycausing short shot. Even when molding is completed, molded productsassume poor surface appearance. In addition, unsatisfactory moldedproducts (exhibiting variation in mass per shot or poor mechanicalproperty such as impact strength) may be produced. Thus, in order toenhance conductivity obtained through addition of a small amount ofconductive filler, enhancement of conductivity of filler itself has beenstudied (see, for example, Japanese Patent Application Laid-Open No.2001-200096).

In an attempt to lower the threshold value, at which conductivitybecomes high and stable through incorporation of a small amount ofconductive filler by virtue of formation of a conductive network formedby the conductive filler in the conductive resin composition, mainly thefollowing three approaches have been studied.

i) Studies on Effects by Shape of Conductive Filler

The studies have elucidated that the threshold value can be loweredthrough reduction of dimensions of conductive filler, increase in aspectratio of the filler or increase in surface area of the filler.

ii) Studies on a Technique of Blending Polymers

With respect to a blended resin having a sea-island structure or amutually continuous structure in the microscopic configuration, therehas been proposed a method for forming a carbon black-matrix resincomposite by incorporating carbon black uniformly into the sea phase(i.e., matrix phase or continuous phase) resin compatible with carbonblack at high concentration and high density (see, for example, JapanesePatent Application Laid-Open No. 02-201811).

Another method has been proposed for forming a CF-matrix resin compositeby incorporating CF uniformly into the sea phase (i.e., matrix phase orcontinuous phase) resin compatible to CF at high concentration anddensity (see, for example, Japanese Patent Application Laid-Open No.01-263156).

iii) An Approach in which the Threshold Value is Lowered by ElevatingInterfacial Energy

It has been elucidated that in a composite composition of any of variousresins and carbon black, the larger the interfacial energy, the smallerthe threshold value (e.g., in a case of polypropylene/carbon black wherethe interfacial energy is higher than a case of nylon/carbon black, thethreshold value is lower). When carbon black is employed as a conductivefiller, there has been made an attempt to elevate interfacial energybetween carbon black and resin by elevating surface energy of carbonblack through oxidation treatment.

The aforementioned studies have been extensively carried out, to therebysteadily lower the threshold value through elevation of conductivity ofconductive filler, by means of the polymer blending method, and othermeans. However, the polymer blending method cannot be applied in thecase where a change in intrinsic properties of a starting materialcaused by blending of polymers is not acceptable. When shape ofconductive filler is fined or the aspect ratio or the surface area ofthe filler is increased, fluidity of the resin composition duringmolding is impaired. The effect of the method for lowering the thresholdvalue by elevating the interfacial energy is not very remarkable. Inthis way, there still remain problems such as deterioration of physicalproperties, lowering of fluidity during molding, poor appearance ofmolded products, in attaining high conductivity of a resin compositionincluding a single resin system.

Specifically, the commercial demand for reducing adhesion of dust onelectric/electronic components to the minimum has been increasing andmore and more intensive year by year, along with the progress ontechnology for downsizing, integration and precision in officeautomation (OA) apparatus and electronic apparatus.

For example, such a demand is even more prominent there in the fields ofIC chips used in semiconductor elements, wafers, interior parts employedin computer hard disks, etc., and adhesion of dust on these parts mustbe completely prevented by imparting antistatic properties to the parts.For such applications, there has been employed, as a conductive resincomposition, a polymer alloy predominantly containing polycarbonateresin (blend of polycarbonate resin with ABS resin) or a polymer alloypredominantly containing polyphenylene ether resin (blend ofpolyphenylene ether resin with polystyrene resin), into which aconductive filler such as carbon black is incorporated. In order toattain high conductivity, a large amount of carbon black must beincorporated into a resin, resulting in a problem that the mechanicalstrength and fluidity of conductive resin are lowered.

With respect to automobile outer parts, “electrostatic coating” isapplied where a coating having an opposite charge added thereto issprayed to a conductivity-imparted resin molded product whileelectrifying the molded product. In the electrostatic coating method,adhesion of the coating onto the surface of molded products is enhancedon the basis of attractive force between the charge on the surface andthe opposite charge in the coating. Many exterior panels and parts ofautomobiles are formed of a polycarbonate resin-polyester resin blend ora polyphenylene ether-polyamide resin blend. When a conductive filler isincorporated into these molding resin materials for impartingconductivity, mechanical strength and fluidity thereof problematicallydecrease.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a production method fora conductive polymer which attains conductivity equal to or higher thanthat of a conventional conductive polymer, through employment of vaporgrown carbon fiber as a conductive filler and incorporation of theconductive filler in an amount smaller than a conventionally employedamount so that mechanical strength may be maintained and the viscosityat the time of kneading may be prevented from increasing, a conductivepolymer obtained by the method and uses of the polymer.

The present inventors have found out that, in order to obtain electricconductivity which is as high as or higher than that of conventionalpolymer with a compounding amount of vapor grown carbon fiber smallerthan in conventional methods, it is important to blend a polymer withcarbon fiber by using a low blending energy under a condition that thepolymer exhibits a melt viscosity under a given value, and havecompleted the present invention based on this finding.

Accordingly, the present invention provides a conductive polymer, and amethod for producing the polymer.

1. A method for producing a conductive polymer, comprising a step ofblending a polymer in a state of a melt viscosity of 600 Pa·s or less ata shear rate of 100 s⁻¹ with a vapor grown carbon fiber in an amount of1 to 15 mass %, at a mixing energy of 1,000 mJ/m³ or less.2. The method for producing a conductive polymer as described in 1above, wherein the polymer is an uncured thermosetting polymer in astate of a melt viscosity of 200 Pa·s or less at a shear rate of 100 s⁻¹and the blending is performed at a mixing energy of 400 mJ/m³ or less.3. The method for producing a conductive polymer as described in 1above, wherein the polymer is a thermoplastic polymer in a state of amelt viscosity of 200 to 600 Pa·s at a shear rate of 100 s⁻¹ and theblending is performed at a mixing energy of 200 to 1,000 mJ/m³.4. The method for producing a conductive polymer as described in any oneof 1 to 3 above, wherein the vapor grown carbon fiber has an outer fiberdiameter of 80 to 500 nm, an aspect ratio of 40 to 1,000, a BET specificsurface area of 4 to 30 m²/g, a d₀₀₂ of 0.345 nm or less as obtainedthrough an X-ray diffraction method, and a ratio (Id/Ig) of 0.1 to 2,wherein Id represents a peak height of a band ranging from 1,341 to1,349 cm⁻¹ and Ig represents a peak height of a band ranging from 1,570to 1,578 cm⁻¹, as observed in a Raman scattering spectrum.5. The method for producing a conductive polymer as described in any oneof 1 to 4 above, wherein the vapor grown carbon fiber has beenheat-treated at 2,000 to 3,500° C. in an inert atmosphere.6. The method for producing a conductive polymer as described in any of1 to 5 above, wherein the vapor grown carbon fiber has a surface energyof 115 mJ/m² or less.7. The method for producing a conductive polymer as described in 6above, wherein the vapor grown carbon fiber has been subjected totreatment for lowering the surface energy by wet- or dry-method.8. The method for producing a conductive polymer as described in 7above, wherein the treatment for lowering the surface energy isfluorination treatment, boron addition treatment or silylationtreatment.9 The method for producing a conductive polymer as described in 2 above,wherein the thermosetting polymer is selected from the group consistingof polyether, polyester, polyimide, polysulfone, epoxy resin,unsaturated polyester resin, phenol resin, urethane resin, urea resinand melamine resin.10 The method for producing a conductive polymer as described in 3above, wherein the thermoplastic polymer is selected from the groupconsisting of polyamide, polyester, liquid crystal polymer,polyethylene, polypropylene, polyphenylene sulfide and polystyrene.11. A method for producing a conductive polymer, comprising a step ofblending a polymer in a state of a melt viscosity of 600 Pa·s or less ata shear rate of 100 s⁻¹ with a vapor grown carbon fiber having a surfaceenergy of 115 mJ/m² or less.12. The method for producing a conductive polymer as described in 11above, wherein the polymer is at least one selected from thermoplasticresins and thermosetting resins being in uncured state.13. The method for producing a conductive polymer as described in 11 or12 above, wherein the vapor grown carbon fiber has been subjected totreatment for lowering the surface energy by wet- or dry-method.14. The method for producing a conductive polymer as described in anyone of 11 to 13 above, wherein the vapor grown carbon fiber has anaverage fiber diameter of 5 μm or less.15. The method for producing a conductive polymer as described in 13above, wherein the treatment for lowering the surface energy isfluorination treatment, boron addition treatment or silylationtreatment.16. A conductive polymer, obtained by the production method described inany one of 1 to 15 above.17. A molded article consisting of conductive polymer obtained by theproduction method described in any one of 1 to 15 above.18. An exterior equipment for automobile, using conductive polymerobtained by the production method described in any one of 1 to 15 above.19. An electromagnetic wave shielding material using conductive polymerproduced by obtained by the production method described in any one of 1or 15 above.20. An antistatic material employing a conductive polymer obtained bythe production method described in any one of 1 or 15 above.21. A conductive adhesive material using a conductive polymer obtainedby the production method described in any one of 1 or 15 above.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will next be described in more detail.

The vapor grown carbon fiber employed in the present invention may beproduced through thermal decomposition of an organic compound in thepresence of an organic transition metal compound.

Examples of the organic compound which can be employed as a raw materialfor producing vapor grown carbon fiber include, in the gas form,toluene, benzene, naphthalene, ethylene, acetylene, ethane, natural gas,carbon monoxide, and mixtures thereof. Of these, aromatic hydrocarbonssuch as toluene and benzene are preferred.

The organic transition metal compound employed in the present inventioncontains a transition metal which serves as a catalyst during thermaldecomposition of an organic compound. Examples of the transition metalcontained in the organic transition metal compound include metalelements of Groups 4 to 10 in the periodic table. Particularly preferredare compounds such as ferrocene or nickelocene.

The vapor grown carbon fiber is produced by mixing the aforementionedorganic compound and the aforementioned organic transition metalcompound with a reducing gas such as hydrogen and feeding the mixtureinto a reactor furnace which is heated at 800 to 1,300° C., therebycausing thermal decomposition.

The thus-produced vapor grown carbon fiber may be hollow along the fiberaxis, or the fiber may be branched. In order to increase compatibilityof the fiber to a matrix resin, the vapor grown carbon fiber ispreferably baked through heat treatment in an inert atmosphere at 900 to1,300° C., thereby removing an organic substance such as tar which hasadhered onto the fiber during a production step. Particularly, in orderto enhance the intrinsic conductivity of the vapor grown carbon fiber,the vapor grown carbon fiber is preferably further heat-treated in aninert atmosphere at 2,000 to 3,500° C., thereby growing graphitecrystals contained in the vapor grown carbon fiber. When the vapor growncarbon fiber is optionally heat-treated, the fiber may be pressed andmolded into a solid compact (e.g., a columnar compact).

No particular limitation is imposed on the furnace for heat treatment ofthe compact, and any furnace such as a typical Acheson-type furnace, aresistance furnace, or a high-frequency furnace may be employed, so longas the furnace can maintain a target temperature of 2,000° C. or higher,preferably 2,300° C. or higher. Alternatively, the compact may be heatedthrough direct passage of electricity. After completion of heating, thecompact is lightly crushed or pulverized, to thereby provide finelydivided carbon fiber products (outer fiber diameter: 80 to 500 nm,aspect ratio: 40 to 1,000: and BET specific surface area: 4 to 30 m²/g).

The atmosphere where the aforementioned heat treatment is performed at2,000° C. or higher is a non-oxidizing atmosphere, preferably a rare gasatmosphere containing one or more species selected from among argon,helium, neon, etc. The time for heat treatment is preferably as short aspossible, from the viewpoint of productivity. When the carbon fibers areheated for a long period of time, the fiber is sintered to besolidified, thereby lowering production yield. Thus, after thetemperature in the core part of the compact has reached the targettemperature, the compact may be maintained at the temperature for onehour or shorter in order to fully attain the object.

It is preferable that the thus-produced carbon fiber be subjected tosurface treatment to thereby reduce the surface energy. Use of vaporgrown carbon fiber with a small surface energy enables a greatenhancement in fluidity of the matrix resin at the time of kneading andmolding steps, which leads to reduction in the shear rate, so that theelectrically conductive network may be maintained.

Specifically, the surface energy of the vapor grown carbon fiber ispreferably 115 mJ/m² or less. Use of vapor grown carbon fiber with thesurface energy exceeding 115 mJ/m² can neither allow reduction in theaddition amount of the vapor grown carbon fiber nor achieve improvementof fluidity. The surface energy of the vapor grown carbon fiber ispreferably 20 to 115 mJ/m², more preferably 30 to 110 mJ/m², still morepreferably 40 to 100 mJ/m².

Measurement of the surface energy is conducted using reverse phasechromatography. The measurement method is specifically described inNippon Gomu Kyokaishi Vol. 67, No. 11, pages 752-759 (1994) published byTHE SOCIETY OF RUBBER INDUSTRY, JAPAN.

Generally, treatment methods for reducing the surface energy of thevapor grown carbon fiber may be classified into dry method (e.g.,discharge treatment or actinic ray treatment) or wet method (e.g.,chemical treatment, polymer-coating, or grafting in the presence of acatalyst). Of these, a dry method is preferred, from the viewpoint ofsimplicity, post treatment, productivity, environmental problems, etc.

Specific examples of the surface treatment method for reducing thesurface energy include direct fluorination, fluorination throughchemical vapor deposition (CVD) (plasma, photo-, or laser), boronaddition treatment, and silylation.

(1) Fluorination

Direct Fluorination

Fluorine is an atom characterized by its remarkably strongelectro-negativity and its size which is the second smallest to hydrogenand its remarkably high reactivity. Thus, carbon fiber can be directlyfluorinated by use of fluorine gas. In order to control reactivity,fluorine gas is generally diluted with an inert gas such as nitrogen orhelium to a concentration of about 0.1 to 5%. Appropriate temperaturecontrol is also critical, and reaction is generally performed at roomtemperature or lower.

Fluorination Through CVD (Plasma, Photo, or Laser)

CVD (chemical vapor deposition) refers to a deposition process in whicha substance present in a gas phase is reacted to deposit as a solidsubstance. Herein, fluorination through a widely used plasma CVDtechnique will be described.

Examples of the plasma apparatus which can be employed include DCplasma, low-frequency plasma, high-frequency plasma, pulse wave plasma,tri-electrode plasma, microwave plasma, downstream plasma, and columnarplasma apparatuses. In addition, an atmospheric plasma apparatus, whichhas been recently developed and attracting attention for its easiness ofoperation, is a useful apparatus.

Surface treatment by fluorination by means of a plasma apparatus can beattained by exposing VGCF to a plasma inert gas atmosphere and treatingthe surface with any of the following treatment gases.

Examples of the treatment gas employable for fluorination in the CVDtechnique include hexafluoroacetone, C₂F₆, C₂F₄, SF₆, CF₄, CF₂Cl₂, CF₃H,NF₃, and fluorine-containing monomers having an F/C ratio of 1.5 orhigher.

No particular limitation is imposed on the excitation source, and inplace of plasma, an excimer beam or laser treatment may also beemployed.

(2) Boron Addition Treatment

Boron addition treatment accelerates crystallization of carbon fiber toreduce the surface energy of the carbon fiber, and to elevateconductivity of the carbon fiber. For example, the treatment may beperformed by a method where boric compound such as boron carbide (B₄C),boron oxide (B₂O₃), boron in elemental state, boric acid (H₃BO₃) orboric acid salt is mixed in the carbon fiber at the time of heattreatment of 2,000° C. to 3,500° C. under an inert atmosphere ofpreferably one or more rare gases of argon, helium and neon.

The boron content added into the carbon fiber, which depends on chemicalproperties and physical properties of the boric compound, is notlimited. For example, in a case where boron carbide (B₄C) is used, thecontent is within a range of 0.05 to 10 mass %, preferably 0.1 to 5 mass% in the amount of the carbon fiber after pulverization.

When the heat treatment is performed in the presence of a boroncompound, the crystallinity of carbon in the carbon fiber increases,thereby elevating conductivity. The boron content in the crystals ofcarbon fiber or on the crystal surface is preferably 0.01 to 5 mass %.In order to enhance conductivity of the carbon fiber and affinity of thecarbon fiber with respect to the resin, the boron content is morepreferably 0.1 mass % or more. Meanwhile, the amount of boron whichsubstitutes carbon atoms forming a graphene sheet (carbon hexagonalnetwork plane) is approximately 3 mass %. Thus, when the boron contentis higher than that amount, particularly 5 mass % or higher, the excessboron remains in the form of boron carbide or boron oxide, which maylower conductivity and is not preferred.

(3) Silylation Treatment

Examples of the treatment gas employable for silylation in the CVDtechnique include hexamethyldisilane, dimethylaminotrimethylsilane, andtetramethylsilane.

In order to enhance affinity of the vapor grown carbon fiber withrespect to the matrix polymer, vapor grown carbon fiber may be oxidized,thereby introducing a phenolic hydroxyl group, a carboxyl group, aquinone group or a lactone group on the surface of the carbon fiber.

Alternatively, the vapor grown carbon fiber may be surface-treated with,for example, a coupling agent (titanate-base, aluminum-base, orphosphate ester-base).

The vapor grown carbon fiber employed in the present invention has anouter fiber diameter of 80 to 500 nm, preferably 90 to 250 nm, morepreferably 100 to 200 nm. When the outer fiber diameter is smaller than80 nm, the surface energy per unit volume exponentially increases,whereby cohesive force among fiber fragments is drastically elevated.The thus-aggregated vapor grown carbon fiber is difficult to disperse ina resin through routine kneading with resin, and fiber aggregates arelocally present in the resin matrix, resulting in failure to form aconductive network. When great shear force is applied to a resin mixtureduring kneading so as to attain good dispersion of carbon fiber,aggregated carbon fiber is broken, and the formed fragments can bedispersed in the resin. However, cutting and rupture of the carbon fiberproceed upon breaking of the aggregates, resulting in failure to attaina desired conductivity.

The vapor grown carbon fiber has an aspect ratio of 40 to 1,000,preferably 50 to 800, more preferably 60 to 500, and particularlypreferably 60 to 200.

When the aspect ratio (i.e., fiber length) increases, fiber filamentsare entangled together, and the thus-formed mass is difficult to bedisentangled, resulting in insufficient dispersion, whereas when theaspect ratio is less than 40, a large amount of filler must beincorporated into a resin so as to form a conductive network structure,leading to remarkable decrease in fluidity and tensile strength of theresin, and both cases are not preferred.

The vapor grown carbon fiber has a BET specific surface area of 4 to 30m²/g, preferably 8 to 25 m²/g, more preferably 10 to 20 m²/g.

When the BET specific surface area increases, the surface energy perunit volume increases, leading to difficulty in dispersion of the carbonfiber in a resin and failure to completely cover the carbon fiber withthe resin. As a result, when a composite is produced from a mixturecontaining such carbon fiber, electroconductivity and mechanicalstrength are deteriorated, which is not preferred.

The interplanar spacing d₀₀₂, as obtained through an X-ray diffractionmethod, is 0.345 nm or less, preferably 0.343 nm or less, morepreferably 0.340 nm or less. As the interplanar spacing d₀₀₂ decreases,crystallinity of graphite increases, thereby elevatingelectroconductivity of the vapor grown carbon fiber, which is preferred.

The ratio (Id/Ig) is 0.1 to 2, preferably 0.15 to 1.5, more preferably0.2 to 1, wherein Id represents a peak height of a band ranging from1,341 to 1,349 cm⁻¹ and Ig represents a peak height of a band rangingfrom 1,570 to 1,578 cm⁻¹, as observed in a Raman scattering spectrum.

In order to obtain high conductivity, crystallinity of vapor growncarbon fiber is preferably high for both the fiber radius direction andthe axial direction. However, when the outer fiber diameter isexcessively small, interplanar spacing may fail to be reduced due to thecurvature. Thus, dispersibility of vapor grown carbon fiber (formationof a conductive network) is also a key factor for forming a conductivenetwork structure which is required to impart conductivity to a resin.Therefore, in order to regulate the dispersibility, surface area perunit volume, aspect ratio, and high crystallinity of the vapor growncarbon fiber are important parameters, and suitable values of outerfiber diameter, aspect ratio, BET specific surface area, interplanarspacing d₀₀₂ as obtained through an X-ray diffraction method, and ratio(Id/Ig) determined from a Raman scattering spectrum are to bedetermined.

No particular limitation is imposed on the polymer employed in thepresent invention, a polymer in a state of a melt viscosity of 600 Pa·sor less at a shear rate of 100 s⁻¹ during kneading with vapor growncarbon fiber is used, which specifically is selected from the groupconsisting of thermosetting resins, photocurable resins andthermoplastic resins. The polymer may be used singly or in combinationof two or more of the species.

Examples of thermosetting resins used in the present invention includepolyether, polyester, polyimide, polysulfone, epoxy resin, unsaturatedpolyester resin, phenol resin, urethane resin, ureic resin and melamineresin.

Examples of thermoplastic resins used in the present invention includeinclude aliphatic and alicyclic polyolefins such as polyethylene,polypropylene, polybutene, and polymethylpentene; aromaticpolycarbonates; polybutylene terephthalate; polyethylene terephthalate;polyphenylene sulfide; polyamides; polyether-imides; polysulfones;polyether-sulfones; polyether-ether-ketones; acrylic resins; styreneresins; modified polyphenylene ethers; and non-olefinic polyethyleneresins such as liquid crystal polyesters.

Among these resins, a resin exhibiting as low a viscosity as possibleduring kneading with vapor grown carbon fiber is preferred. In thisconnection, thermosetting resin is preferred, from the viewpoint ofkneadability at low viscosity. In terms of thermoplastic resins, resinshaving a low melt viscosity, such as polyamides, polyesters, liquidcrystal polymers, polyethylene, polypropylene, and polystyrene, arepreferred.

Meanwhile, vapor grown carbon fiber is remarkably stable to temperatureupon kneading and may be kneaded at high temperature. Therefore, theresin mixture can be kneaded at an elevated temperature so as to reduceviscosity of the resin, so long as the resin does not undergodeterioration, decomposition, or any adverse change in quality.

Conductive polymers may be produced through a method including kneadingcomponents by means of a customary apparatus such as an extruder or akneader. Examples of the method for molding thermoplastic resin includepress molding, extrusion, vacuum molding, blow molding, and injectionmolding. Examples of the method for molding thermosetting resin includetransfer molding.

The energy applied to mixing (kneading) of the polymer and the vaporgrown carbon fiber is 1,000 mJ/m³ or less, so as to prevent cutting andlocalized dispersion of the vapor grown carbon fiber, preferably 50 to1,000 mJ/m³, more preferably 50 to 800 mJ/m³, still more preferably 50to 500 mJ/m³.

The mixing energy is determined predominantly from the following threefactors: viscosity of a composition containing a polymer and vapor growncarbon fiber at a given kneading temperature; a rotation rate of akneader; and a kneading time. Thus, kneading is preferably performed atlow viscosity and low rotation rate for a short period of time. However,when mixing is performed at 50 mJ/m³ or less, variation (lack ofuniformity) in concentration of vapor grown carbon fiber contained inthe matrix cannot be eliminated, thereby deteriorating reliability inproduct characteristics, which is nor preferred. When the mixing energyis 1,000 mJ/m³ or higher, diffusion, cutting, and localized dispersionof the vapor grown carbon fiber occur, resulting in failure to attaindesired characteristics.

In a case where the matrix polymer is a thermosetting polymer,particularly where the polymer in a state of a melt viscosity of 200Pa·s or less at a shear rate of 100 s⁻¹ is mixed, it is preferable thatthe mixing energy be 400 mJ/m³ or less. In a case where the matrixpolymer is a thermoplastic polymer, particularly where the polymer in astate of a melt viscosity of 200 to 600 Pa·s at a shear rate of 100 s⁻¹is mixed, it is preferable that the mixing energy be 200 to 1,000 mJ/m³.

Into the thus-produced conductive plastic composition, vapor growncarbon fiber is incorporated in an amount of 1 to 15 mass %, preferably5 to 10 mass %, so as to attain a volume resistivity of 10 to 10⁸ Ω·cm,preferably 10² to 10⁵ Ω·cm.

When the vapor grown carbon fiber content is less than 1 mass %, theconductivity of the resultant plastic composition is insufficient,whereas when the content is in excess of 15 mass %, conductivity may besatisfactory, but problems such as inevitable increase in cost, decreasein plastic characteristics, and inhibition of flow of resin duringextrusion or injection molding arise.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will next be described in more detail by way ofExamples and Comparative Examples.

EXAMPLES 1 TO 6 AND COMPARATIVE EXAMPLES 1 AND 2

<Methods of Measurement>

i) Outer Fiber Diameter

Mean diameter (outer diameter) of the vapor grown carbon fiber wasderived by observing the fiber under a scanning electron microscope(×20,000) as 30 visible images, measuring the outer fiber diameters of300 fiber filaments by means of an image analyzer (LUZEX-AP, product ofNireco), and averaging the values.

ii) Aspect Ratio

The aspect ratio was calculated by mean fiber length/mean fiber diameterof the vapor grown carbon fiber. The mean fiber length was derived byobserving the fiber under a scanning electron microscope (×2,000) as 30visible images and measuring the fiber diameters of 300 fiber filamentsby means of an image analyzer.

iii) BET Specific Surface Area

BET specific surface area was determined through a nitrogen gasadsorption method (by means of NOVA 1000, product of Yuasa Ionics Inc.).

iv) d₀₀₂ Value Determined Through X-ray Diffraction Method

d₀₀₂ Values were determined through powder X-ray diffraction (by meansof Rigaku Geigerflex) while Si was used as an internal standard.

v) Ratio (Id/Ig) Determined from a Raman Scattering Spectrum

The ratio (Id/Ig), wherein Id represents a peak height of a band rangingfrom 1,341 to 1,349 cm⁻¹ and Ig represents a peak height of a bandranging from 1,570 to 1,578 cm⁻¹ as determined from a Raman scatteringspectrum was determined by means of a Raman spectrometer (LabRam HR,product of Jobin Yvon).

The method for producing vapor grown carbon fiber A employed in theExamples and characteristics of carbon fiber A will be described below.Firstly, a raw material liquid was prepared by mixing benzene,ferrocene, and sulfur in proportions (by mass) of 91:7:2. The rawmaterial liquid was fed with hydrogen serving as a carrier gas to areaction furnace (inner diameter: 100 mm, height: 2,500 mm) heated at1,200° C. and sprayed. The feed rates of the raw material and thehydrogen flow were adjusted to 10 g/min and 60 L/min, respectively. Thereaction product (150 g) obtained through the above method was chargedinto a graphite crucible (inner diameter: 100 mm, height: 10 mm), bakedat 1,000° C. for one hour under argon, and subsequently, graphitized at2,800° C. for one hour under argon, to thereby produce vapor growncarbon fiber A.

The vapor grown carbon fiber A was found to have a mean fiber diameterof 150 nm, a mean fiber length of 9.0 μm, an aspect ratio of 60, a BETspecific surface area of 13 m²/g, a d₀₀₂ of 0.339 nm, and an Id/Ig of0.2.

The method for producing vapor grown carbon fiber B employed in theExamples and characteristics of carbon fiber B will be described below.Firstly, a raw material liquid was prepared by mixing benzene,ferrocene, and sulfur in proportions (by mass) of 97:2:1. The rawmaterial liquid was fed with hydrogen serving as a carrier gas to areaction furnace (inner diameter: 100 mm, height: 2,500 mm) heated at1,200° C. and sprayed. The feed rates of the raw material and thehydrogen flow were adjusted to 5 g/min and 90 L/min, respectively.

The reaction product (150 g) obtained through the above method wascharged into a graphite crucible (inner diameter: 100 mm, height: 150mm), baked at 1,000° C. for one hour under argon, and subsequently,graphitized at 2,800° C. for one hour under argon, to thereby producevapor grown carbon fiber B.

The vapor grown carbon fiber B was found to have a mean fiber diameterof 80 nm, a mean fiber length of 12.0 μm, an aspect ratio of 150, a BETspecific surface area of 25 μm²/g, a d₀₀₂ of 0.340 nm, and an Id/Ig of0.14.

The method for producing vapor grown carbon fiber C employed in theExamples and characteristics of carbon fiber C will be described below.Firstly, a raw material liquid was prepared by mixing benzene,ferrocene, and sulfur in proportions (by mass) of 92:6:2. The rawmaterial liquid was heated and vaporized by using a 300° C.-evaporator.Thus prepared raw material gas was fed with hydrogen serving as acarrier gas to a reaction furnace (inner diameter: 100 mm, height: 2,500mm) heated at 1,200° C. The feed rates of the raw material and thehydrogen flow were adjusted to 8 g/min and 60 L/min, respectively. Thereaction product (150 g) obtained through the above method was chargedinto a graphite crucible (inner diameter: 100 mm, height: 150 mm), bakedat 1,000° C. for one hour under argon, and subsequently, graphitized at2,800° C. for one hour under argon, to thereby produce vapor growncarbon fiber C (hereinafter, sometimes referred to as “VGCF-S”).

The vapor grown carbon fiber C(VGCF-S) was found to have a mean fiberdiameter of 100 nm, a mean fiber length of 13.0 μm, an aspect ratio of130, a BET specific surface area of 20 m²/g, a d₀₀₂ of 0.340 nm, and anId/Ig of 0.14.

Method for Evaluating Polymer

With respect to the volume resistivity of 10⁸ Ω·cm or less of each resincomposition, measurement was performed through the four-probe method (bymeans of Loresta HP MCP-T410, product of Mitsubishi Chemical Industries,Ltd.) and With respect to the volume resistivity of 10⁸ Ω·cm or more,measurement was performed by use of an insulation resistance tester(ultra-high resistance/micro current meter R8340, product of ADVANTEST).

Each molded product of the conductive polymer was fired at 1,000° C. for30 minutes under argon, thereby collecting vapor grown carbon fiber. Thethus-collected vapor grown carbon fiber was observed under a scanningelectron microscope, and an average fiber length was derived throughimage analysis, whereby the degree of fiber cutting due to kneading wasevaluated.

The viscosity (fluidity) of the matrix polymer and composition wasmeasured by using a Capirograph (a capillary type rheometer).

EXAMPLE 1

Polypropylene resin (Sun-Allomer PWB02N (MFI: 70), product of SunAllomerLtd.) (90 mass %) and vapor grown carbon fiber A (10 mass %) weremelt-kneaded by means of Laboplast mill R100 (product of Toyo SeikiSeisakusho, Ltd.) at 200° C. and 40 rpm for 5 minutes (kneading energy:200 mJ/m³). The kneaded product was molded by means of a 50-ton thermalmolding apparatus (product of Nippo Engineering) at 200° C. and 200kgf/cm² for 30 seconds, to thereby produce 10 mm×10 mm×2 mm t platesamples. The matrix resin had a melt viscosity of 100 Pa·s at a shearrate of 100 s⁻³ at a temperature of 200° C.

EXAMPLE 2

Polyamide 6 resin (Novamid 1010, product of Mitsubishi ChemicalIndustries, Ltd.) (90 mass %) and vapor grown carbon fiber A (10 mass %)were melt-kneaded by means of Laboplast mill R100 (product of Toyo SeikiSeisakusho, Ltd.) at 260° C. and 40 rpm for 10 minutes (kneading energy:500 mJ/m³). The kneaded product was molded by means of a 50-ton thermalmolding apparatus (product of Nippo Engineering) at 200° C. and 200kgf/cm² for 30 seconds, to thereby produce 10 mm×10 mm×2 mm t platesamples. The matrix resin had a melt viscosity of 80 Pa·s at a shearrate of 100 s⁻¹ at a temperature of 260° C.

EXAMPLE 3

Polypropylene resin (Sun-Allomer PWB02N (MFI: 70), product of SunAllomerLtd.) (54 mass %), polyethylene resin (J-Rex HD KMA90K (MFI: 30),product of Japan Polyolefins Co., Ltd.) (46 mass %), and vapor growncarbon fiber A (10 mass %) were melt-kneaded by means of Laboplast millR100 (product of Toyo Seiki Seisakusho, Ltd.) at 180° C. and 40 rpm for5 minutes (kneading energy: 180 mJ/m³). The kneaded product was moldedby means of a 50-ton thermal molding apparatus (product of NippoEngineering) at 200° C. and 200 kgf/cm² for 30 seconds, to therebyproduce 10 mm×10 mm×2 mm t plate samples. The matrix resin had a meltviscosity of 150 Pa·s at a shear rate of 100 s⁻¹ at a temperature of180° C.

EXAMPLE 4

Polypropylene resin (Sun-Allomer PWB02N (MFI: 70), product of SunAllomerLtd.) (95 mass %) and vapor grown carbon fiber B (5 mass %) weremelt-kneaded by means of Laboplast mill R100 (product of Toyo Seiki) at200° C. and 40 rpm for 5 minutes (kneading energy: 150 mJ/m³). Thekneaded product was molded by means of a 50-ton thermal moldingapparatus (product of Nippo Engineering) at 200° C. and 200 kgf/cm² for30 seconds, to thereby produce 10 mm×10 mm×2 mm t plate samples. Thematrix resin had a melt viscosity of 100 Pa·s at a shear rate of 100 s⁻¹at a temperature of 200° C.

EXAMPLE 5

Epoxy resin (EPICLON HP-7200, product of Dainippon Ink and Chemicals,Inc.) (90 mass %) and vapor grown carbon fiber A (10 mass %) weremelt-kneaded by means of Laboplast mill R100 (product of Toyo SeikiSeisakusho, Ltd.) at 80° C. and 40 rpm for 5 minutes (kneading energy:100 mJ/m³). The kneaded product was molded by means of a 50-ton thermalmolding apparatus (product of Nippo Engineering) at 175° C. and 100kgf/cm² for 5 hours, to thereby produce 10 mm×10 mm×2 mm t platesamples. The matrix resin had a melt viscosity of 30 Pa·s at a shearrate of 100 s⁻¹ at a temperature of 80° C.

EXAMPLE 6

Polypropylene resin (Sun-Allomer PWB02N, product of SunAllomer Ltd.) (95mass %) and vapor grown carbon fiber C (5 mass %) were melt-kneaded bymeans of Laboplast mill R100 (product of Toyo Seiki Seisakusho, Ltd.) at200° C. and 40 rpm for 5 minutes (kneading energy: 150 mJ/m³). Thekneaded product was molded by means of a 50-ton thermal moldingapparatus (product of Nippo Engineering) at 200° C. and 200 kgf/cm² for30 seconds, to thereby produce 10 mm×10 mm×2 mm t plate samples. Thematrix resin had a melt viscosity of 100 Pa·s at a shear rate of 100 s⁻¹at a temperature of 200° C.

COMPARATIVE EXAMPLE 1

Polypropylene resin (Sun-Allomer PWB02N (MFI: 70), product of SunAllomerLtd.) (90 mass %) and vapor grown carbon fiber A (10 mass %) weremelt-kneaded by means of Laboplast mill R100 (product of Toyo SeikiSeisakusho, Ltd.) at 180° C. and 40 rpm for 20 minutes (kneading energy:1,100 mJ/m³). The kneaded product was molded by means of a 50-tonthermal molding apparatus (product of Nippo Engineering) at 200° C. and200 kgf/cm² for 30 seconds, to thereby produce 10 mm×10 mm×2 mm t platesamples. The matrix resin had a melt viscosity of 150 Pa·s at a shearrate of 100 s⁻¹ at a temperature of 180° C.

COMPARATIVE EXAMPLE 2

Polypropylene resin (Sun-Allomer PWB02N (MFI: 70), product of SunAllomerLtd.) (90 mass %) and vapor grown carbon fiber A (10 mass %) weremelt-kneaded by means of Laboplast mill R100 (product of Toyo SeikiSeisakusho, Ltd.) at 170° C. and 80 rpm for 20 minutes (kneading energy:3,000 mJ/m³). The kneaded product was molded by means of a 50-tonthermal molding apparatus (product of Nippo Engineering) at 200° C. and200 kgf/cm² for 30 seconds, to thereby produce 10 mm×10 mm×2 mm t platesamples. The matrix resin had a melt viscosity of 180 Pa·s at a shearrate of 100 s⁻¹ at a temperature of 170° C.

The results of Examples 1 to 6 and Comparative Examples 1 and 2 areshown in Table 1.

TABLE 1 Mean Knead- length of Raw ing Type Volume collected materialenergy of Amount resistivity fiber resin (mJ/m³) VGCF mass % (Ω · cm)(μm) Ex. 1 PP*¹ 200 A 10 9.5 × 10² 8.8 Ex. 2 PA6*² 500 A 10 3.9 × 10⁵8.5 Ex. 3 PP/PE*³ 180 A 10 1.0 × 10² 8.8 Ex. 4 PP 150 B 5 1.1 × 10² 11.8Ex. 5 Epoxy*⁴ 100 A 10 8.4 × 10² 8.7 Ex. 6 PP 150 C 5 2.0 × 10² 12.5Comp. PP 1,100 A 10 1.5 × 10¹⁰ 7.3 Ex. 1 Comp. PP 3,000 A 10 4.2 × 10¹⁵6.5 Ex. 2 *¹Polypropylene (Sun-Allomer PB02N, product of SunAllomerLtd.) *²Polyamide 6 (Novamid 1010, product of Mitsubishi ChemicalIndustries, Ltd.) *³A mixture of polypropylene (Sun-Allomer PB02N,product of SunAllomer Ltd.) (54 mass %) and polyethylene (J-Rex HDKMA90K, product of Japan Polyethylene Co., Ltd.) (46 mass %) *⁴Epoxyresin (EPICLON HP-7200, product of Dainippon Ink and Chemicals, Inc.)

EXAMPLES 7 TO 14 AND COMPARATIVE EXAMPLES 3 TO 8 VGCF

As vapor grown carbon fiber, VGCF (registered trademark) (product ofShowa Denko K.K., average fiber diameter:150 nm, average fiber length:9μm, aspect ratio:60, BET specific surface area:13 m²/g, d₀₀₂=0.339 nm,and Id/Ig=0.2) was used. The same VGCF was also employed in surfacetreatment.

VGCF-S

As vapor grown carbon fiber, VGCF-S (average fiber diameter:100 nm,average fiber length:13 μm, aspect ratio:130, BET specific surfacearea:20 m²/g, d₀₀₂=0.340 nm, and Id/Ig=0.14) was used. The same VGCF-Swas also employed in surface treatment.

Surface Treatment Method

(1) Fluorination Treatment

A plasma powder treatment device (product of Samco InternationalKenkyusho) was employed.

In a sample flask where plasma was to be generated, vapor grown carbonfiber was placed together with argon serving as a carrier gas and CF₄serving as a reactive gas, and the gas pressure was adjusted to 1 Torr.The vapor carbon grown fiber was surface-treated in the flask by meansof a high-frequency power source of a frequency of 13.54 MHz at adischarge power of 200 W for 60 seconds.

(2) Boron Addition Treatment

B₄C powder (mean particle size: 15 μm) (120 g) was added to vapor growncarbon fiber (2.88 kg), and the mixture was sufficiently mixed by meansof a Henschel mixer. The mixture was charged into a cylindrical graphitecrucible (volume: 50 L) and pressed, thereby adjusting the bulk densityto 0.07 g/cm³. The crucible was closed with a lid while the compact waspressurized with a graphite pressure sheet and transferred to anAcheson-type furnace for heat treatment. The heat treatment temperaturewas 2,900° C., and the treatment was continued at the temperature for 60minutes. After completion of heat treatment and subsequent cooling, thetreated vapor grown carbon fiber was removed from the crucible andpulverized by means of a Bantam mill. Non-fibrous matter was removed bymeans of an air classifier. The fiber diameter of the thus-obtainedfiber remained unchanged through treatment.

(3) Silylation Treatment

A plasma powder treatment device (product of Samco InternationalKenkyusho) was employed.

Vapor grown carbon fiber was placed in a sample flask together withargon serving as a carrier gas and tetramethylsilane serving as areactive gas and the gas pressure was adjusted to 1 Torr. The vaporgrown carbon fiber was surface-treated in the flask by means of ahigh-frequency power source of a frequency of 13.54 MHz at a dischargepower of 200 W for 60 seconds (gas pressure: 1 Torr).

Determination of Surface Energy

Measurement of the surface energy was conducted using reverse phasechromatography as described in Nippon Gomu Kyokaishi Vol. 67, No. 11,pages 752-759 (1994) published by THE SOCIETY OF RUBBER INDUSTRY, JAPAN.According to this method, surface free energy (surface tension) can bemeasured regardless of the shape of the samples in a relatively simplemanner and high precision in measurement can be attained. Specifically,the measurement was performed as follows.

Each of vapor grown carbon fiber samples serving as an adsorption phasewas charged into a glass column (inner diameter: 3 mm, length: 2.1 m).Measurement was carrier out by use of a gas chromatograph GC-7A(detector: TCD) (product of Shimadzu Corporation) with helium serving asa carrier gas at a column temperature of 90° C. in order to evaluatedispersion performance, each of n-alkane:pentane, hexane, and heptanewas employed as a probe. In order to evaluate polarity, each of benzeneand tetrahydrofuran was employed as a basic solution, and each ofdichloromethane and chloroform was employed as an acidic solution.

Table 2 shows measurement results of surface energy values of vaporgrown carbon fiber and surface-treated vapor grown carbon fiber.

TABLE 2 Surface energy of carbon fiber and surface-treated carbon fiberType of carbon fiber Surface energy (mJ/m²) VGCF 119 Boron-treated VGCF98 Fluorinated VGCF 85 Silylated VGCF 90 VGCF-S 120 Fluorinated VGCF-S84Kneading Method

Laboplast mill (volume: 100 ml) (product of Toyo Seiki) was employed asa kneader.

Generally, Laboplast mill is employed for assessing processingcharacteristics of a polymer such as thermoplastic resin, thermosettingresin, or elastomer on the basis of a mixing test.

In a sample kneading portion of the heated mixer, two kneading blades,which are rotatable in directions different from each other at differentrotating ratios, and a resin temperature detector are provided.

The resin fed to the mixer is kneaded by accepting shear, and melting ofthe resin and dispersion of the filler occur as kneading proceedsdepending on the characteristics of the resin and filler. The feature ofmelting and dispersing can be detected as a torque applied to theblades. When a resin having a high melt viscosity is used, aconsiderably high torque; i.e., high shear stress, is applied to themixture, thereby uniformly dispersing the filler.

Molding Method

i) Thermoplastic Resin

Each thermoplastic resin was molded into plate pieces (100×100×2 mm) bymeans of an injection molding machine (Sicap, clamping force 75 tons,product of Sumitomo Heavy Industries, Ltd.) at a cylinder temperatureshown in Table 2. PP, PA6, and PPS were molded at a mold temperature of20° C., 40° C., and 120° C., respectively.

ii) Thermosetting Resin

Each thermosetting resin was molded into plate pieces (100×100×2 mm) bymeans of a molding machine (M-70C-TS, product of Meiki Co., Ltd.). Allylester was molded at a cylinder temperature of 80° C. and a moldtemperature of 160° C. for a retention time of 10 minutes.

Resins Employed

i) Thermoplastic Resin

Polypropylene (PP), Products of SunAllomer Ltd.

PM 900A (MI=30)

PW 201N (MI=0.6)

Polyamide 6 (PA6), Product of Toray Industries, Inc.

Amilan CM 1007

Polyphenylene sulfide (PPS), Product of Toso Corporation

Susteel F11

ii) Thermosetting Resin

Allyl ester Resin, Product of Showa Denko K.K.

AA 101 (viscosity: 630,000 cps (30° C.)), employed organic peroxide:dicumyl peroxide (Percumyl D, product of Nippon Oil & Fats Co., Ltd.)

Melt viscosity values (at a shear rate of 100 s⁻¹) of employed resinsare shown in Table 3.

TABLE 3 Melt viscosity at shear rate of 100 s⁻¹ Melt viscosity Moldingtemp. Resin Grade Pa · s ° C. PP PM 900A 150 220 PW 201N 1,000 220 600280 PA6 CM 1007 100 240 PPS F11 200 320 Allyl ester AA 101 100 60Evaluation of Physical PropertiesMeasurement of Physical Properties

Volume resistivity was determined in accordance with a four-probe method(JIS K7194).

Bending characteristics of the samples were evaluated in terms ofthree-point bending strength (test piece: 100×10×2 mm, span interval: 64mm, and bending speed: 2 mm/min).

Measurement of Viscosity (Capirograph)

A Capirograph is a capillary type rheometer and is employed formeasurement as stipulated in JIS K7119. Through employment of thisrheometer, fluidity of each matrix polymer and each composition weredetermined. Table 3 shows the measurement results with respect to matrixpolymers, and Tables 4 and 5 show the results with respect to resincompositions.

The results of the Examples and those of the Comparative Examples areshown in Tables 4 and 5, respectively.

TABLE 4 Results of the Examples amount Resin, of grade, Type of carbonVol. Melt Bending molding carbon fiber resistivity viscosity strengthEx. temp. fiber (mass %) (Ω · cm) (Pa · s) (Mpa) Ex. 7 PP Boron-added 53 × 10⁰ 200 55 PM 900A VGCF 220° C. Ex. 8 PP Fluorinated 5 4 × 10⁰ 18052 PM 900A VGCF 220° C. Ex. 9 PP Silylated 5 1 × 10¹ 190 50 PM 900A VGCF220° C. Ex. 10 PP Boron-added 5 5 × 10² 550 50 PW 201N VGCF 280° C. Ex.11 PA6 Fluorinated 10 2 × 10² 200 120 CM 1007 VGCF 240° C. Ex. 12 PPSBoron-added 10 1 × 10⁰ 300 75 F11 VGCF 320° C. Ex. 13 Allyl Silylated 52 × 10² 150 80 ester VGCF AA 101 60° C. Ex. 14 PP Fluorinated 2 3 × 10¹180 50 PM900A VGCF-S 220° C.

TABLE 5 Results of the Comparative Examples Resin, amount of grade, Typeof carbon Vol. Melt Bending Comp. molding carbon fiber resistivityviscosity strength Ex. temp. fiber (mass %) (Ω · cm) (Pa · s) (Mpa)Comp. PP VGCF 5 3 × 10¹⁰ 250 50 Ex. 3 PM 900A 220° C. Comp. PP B-added10 5 × 10¹⁵ 1,100 50 Ex. 4 PW 201N VGCF 220° C. Comp. PA6 VGCF 10 1 ×10¹² 300 100 Ex. 5 CM 1007 240° C. Comp. PPS VGCF 10 5 × 10⁸ 400 60 Ex.6 F11 320° C. Comp. Allyl VGCF 5 3 × 10¹² 200 70 Ex. 7 ester AA 101 60°C. Comp. PP VGCF-S 2 3 × 10⁴ 1100 45 Ex. 8 PW210N 220° C.

Table 6 shows threshold values of various vapor grown carbon fibers atdifferent molding temperature.

When a composite material containing polypropylene (PM 900A) and VGCFwas molded at 220° C., the threshold value was found to be 7%. In otherwords, high conductivity was obtained (conductive network was formed)when the amount of VGCF added reached 7%. When a modified VGCF(boron-added, fluorinated, or silylated) whose surface energy had beenlowered was used, the threshold value was reduced to 3%, exhibiting theeffect of the invention.

When a composite material containing polypropylene (PW 201N) andboron-added VGCF was molded at 220° C., a conductive network was brokendue to high melt viscosity, thereby elevating the threshold value to15%. However, when the molding temperature was elevated, the thresholdvalue could be reduced to 4% by virtue of lowered melt viscosity.

When a composite material containing polyamide 6 and VGCF was molded at240° C., the threshold value was found to be 13%. However, whenfluorinated VGCF was used, the threshold value was reduced to 8%,exhibiting the effect of reduced surface energy.

When a composite material containing polyphenylene sulfide and VGCF wasmolded at 320° C., the threshold value was found to be 10%. However,when boron-added VGCF was used, the threshold value was reduced to 7%.

In the case of a composite material containing a thermosetting allylester and VGCF, the threshold value was found to be 8%. However, whensilylated VGCF was used, the threshold value was reduced to 3%,exhibiting the effect of reduced surface energy on VGCF.

When a composite material containing polypropylene (PW210N) and VGCF-Swas molded at 220° C., the threshold value was found to be 3%. However,when a fluorinated VGCF-S having a reduced surface energy was used, thethreshold value was reduced to 1.5%, which showed that use of such afluorinated VGCF-S was effective.

TABLE 6 Type of vapor grown carbon fiber, molding temperature, andthreshold values of resins Type of carbon Molding Threshold fiber Resin,grade temp. value VGCF PP, PM 900A 220° C. 7% B-added VGCF PP, PM 900A220° C. 3% Fluorinated VGCF PP, PM 900A 220° C. 3% Silylated VGCF PP, PM900A 220° C. 3% B-added VGCF PP, PW 201N 220° C. 15%  B-added VGCF PP,PW 201N 280° C. 4% VGCF PA6, CM 1007 240° C. 13%  Fluorinated VGCF PA6,CM 1007 240° C. 8% VGCF PPS, F11 320° C. 10%  B-added VGCF PPS, F11 320°C. 7% VGCF Allyl ester, AA 101  60° C. 8% Silylated VGCF Allyl ester, AA101  60° C. 3% VGCF-S PP PW201N 220° C. 3% VGCF-S PP PW201N 220° C.1.5%  

INDUSTRIAL APPLICABILITY

The conductive polymer of the present invention uses as a conductivityimparting agent, a vapor grown carbon fiber which is excellent ineconomical efficiency and a mass supply of which is available. In theconductive polymer, cutting of vapor grown carbon fiber can be reducedthrough the control of kneading energy at the time of kneading matrixpolymer and the vapor grown carbon fiber and thus a conductive networkstructure is formed and maintained, as a result, the polymer obtained byincorporating a small amount of vapor grown carbon fiber can exhibitexcellent conductivity. Therefore, the polymer maintains its intrinsicfluidity and provides excellent molded products. In addition, since thevapor grown carbon fiber is added only in a small amount, decrease inmechanical strength can be suppressed to a minimum level, therebyproviding products of high reliability.

The conductive polymer of the present invention, which is excellent inelectric properties such as conductivity and antistatic property, andfurther in surface smoothness, dimension precision, glossiness,mechanical strength, coatability, heat stability and impact resistance,is useful in many industrial fields, such as the field of material forshipping or wrapping electronic components, the field of components ofoffice automation (OA) apparatus and electronic apparatus and the fieldof antistatic coating material for automobile.

1. A method for producing a conductive polymer, comprising a step ofblending a polymer in a state of a melt viscosity of 600 Pa·s or less ata shear rate of 100 s⁻¹ with a vapor grown carbon fiber in an amount of1 to 15 mass %, at a mixing energy of 1,000 mJ/m³ or less, wherein saidstep of blending comprises melt kneading at 80° C. to 260° C.
 2. Themethod for producing a conductive polymer as claimed in claim 1, whereinthe polymer is an uncured thermosetting polymer in a state of a meltviscosity of 200 Pa·s or less at a shear rate of 100 s⁻¹ and theblending is performed at a mixing energy of 400 mJ/m³ or less.
 3. Themethod for producing a conductive polymer as claimed in claim 1, whereinthe polymer is a thermoplastic polymer in a state of a melt viscosity of200 to 600 Pa·s at a shear rate of 100 s⁻¹ and the blending is performedat a mixing energy of 200 to 1,000 mJ/m³.
 4. The method for producing aconductive polymer as claimed in claim 1, wherein the vapor grown carbonfiber has an outer fiber diameter of 80 to 500 nm, an aspect ratio of 40to 1,000, a BET specific surface area of 4 to 30 m₂/g, a d⁰⁰² of 0.345nm or less as obtained through an X-ray diffraction method, and a ratio(Id/Ig) of 0.1 to 2, wherein Id represents a peak height of a bandranging from 1,341 to 1,349 cm⁻¹ and Ig represents a peak height of aband ranging from 1,570 to 1,578 cm⁻¹, as observed in a Raman scatteringspectrum.
 5. The method for producing a conductive polymer as claimed inclaim 1, wherein the vapor grown carbon fiber has been heat-treated at2,000 to 3,500° C. in an inert atmosphere.
 6. The method for producing aconductive polymer as claimed in claim 1, wherein the vapor grown carbonfiber has a surface energy of 115 mJ/m² or less.
 7. The method forproducing a conductive polymer as claimed in claim 6, wherein the vaporgrown carbon fiber has been subjected to treatment for lowering thesurface energy by wet- or dry-method.
 8. The method for producing aconductive polymer as claimed in claim 7, wherein the treatment forlowering the surface energy is fluorination treatment, boron additiontreatment or silylation treatment.
 9. The method for producing aconductive polymer as claimed in claim 2, wherein the thermosettingpolymer is selected from the group consisting of polyether, polyester,polyimide, polysulfone, epoxy resin, unsaturated polyester resin, phenolresin, urethane resin, urea resin and melamine resin.
 10. The method forproducing a conductive polymer as claimed in claim 3, wherein thethermoplastic polymer is selected from the group consisting ofpolyamide, polyester, liquid crystal polymer, polyethylene,polypropylene, polyphenylene sulfide and polystyrene.
 11. A method forproducing a conductive polymer, comprising a step of blending a polymerin a state of a melt viscosity of 600 Pa·s or less at a shear rate of100 s⁻¹ with a vapor grown carbon fiber having a surface energy of 115mJ/m², at a mixing energy of 1,000 mJ/m³ or less, wherein said step ofblending comprises melt kneading at 80° C. to 260° C.
 12. The method forproducing a conductive polymer as claimed in claim 11, wherein thepolymer is at least one selected from thermoplastic resins andthermosetting resins being in uncured state.
 13. The method forproducing a conductive polymer as claimed in claim 11, wherein the vaporgrown carbon fiber has been subjected to treatment for lowering thesurface energy by wet- or dry-method.
 14. The method for producing aconductive polymer as claimed in claim 11, wherein the vapor growncarbon fiber has an average fiber diameter of 5 μm or less.
 15. Themethod for producing a conductive polymer as claimed in claim 13,wherein the treatment for lowering the surface energy is fluorinationtreatment, boron addition treatment or silylation treatment.